1. Field of the Invention
The present invention relates generally to a magnetic field generator, and more specifically to such a generator for effectively confining magnetron plasma which is produced within a vacuum chamber in which a workpiece is positioned so as to be subject to plasma treatment.
2. Description of Related Art
It is known in the art to generate magnetron plasma, within an evacuated process chamber (viz., vacuum chamber), for use in implementing plasma treatment such as etching, film growth, etc. on the workpiece such as a semiconductor wafer provided in the chamber.
Prior to turning to the present invention, it is deemed advantageous to briefly describe, with reference to FIG. 1, a conventional magnetic field generator via which the plasma produced within the vacuum chamber is confined, When performing the plasma treatment (processing) on the workpiece, it is vital to effectively confine plasma in a manner to surround the workpiece so as to obtain designed results.
As shown in FIG. 1, a semiconductor wafer (viz., workpiece) 10 is positioned at the center area of a vacuum chamber 12 in a manner to face the surface of the workpiece upward on which the plasma treatment is to be carried out. Although not shown in FIG. 1, plasma is generated within the vacuum chamber 12 by way of conventional technology. The plasma generation per se is not directly concerned with the present invention, and thus the further description thereof will be omitted for the sake of simplifying the instant disclosure.
In order to effectively confine plasma around the workpiece 10 with forming no magnetic field above the wafer 10 (or with permitting very week magnetic field above the wafer), a magnetic field generator (or multi-pole magnet unit) 14 is provided outside the vacuum chamber 12. The magnetic field generator 14 is comprised of a ring-like magnetic member (supporter) 16 and a plurality of segment type permanent magnets (hereinafter referred to as segment magnets) 18 attached to the inner side of the member 16. More specifically, the segment magnets 18 are arranged such as to alternately change the magnetic polarities thereof in the circumferential direction of the supporter 16, and thus, a multi-pole magnetic field is generated within the vacuum chamber 12 so as to confine the plasma around the workpiece 10. Small arrows on the segment magnets 18 respectively indicate the magnetized directions of the magnets 18, and curved lines 20 respectively indicate magnetic forth lines.
It is typical in the art, when constructing the magnetic field generator 14, to make use of the permanent magnets 18 rather than electromagnets because the electric power consumption can be zeroed and the structure of the apparatus can be simplified. On the other hand, a study made by the inventor of the instant application has revealed that the plasma treatment rate (i.e., etch rate) on the wafer surface depends on the strength of the multi-pole magnetic field. However, there has been no proposal to control the multi-pole magnetic field which is generated using a multiple of permanent magnets. In other words, a permanent magnet type conventional magnetic field generator is unable to adaptively control the magnetic field strength.
It is therefore an object of the present invention to provide a magnetic field generator wherein the strength of the multi-pole magnetic field generated thereby can adaptively be controlled.
One aspect of the present invention resides in a magnetic field generator for generating a multi-pole magnetic field around a workpiece positioned within a vacuum chamber. The magnetic field generator is provided outside the vacuum chamber and comprises a plurality of segment type permanent magnets circularly arranged. The magnetic field generator further comprises a plurality of magnetic members to which the segment magnets are selectively attached.